1. Field of the Invention
The present invention relates to a method of manufacturing an electrode plate assembly for a lead accumulator and a device therefor by which the electrode plate assembly of a lead accumulator is manufactured by forming a strap connecting electrode plates on an electrode plate group constituted by stacking a plurality of electrode plates, as well as by joining pillar electrodes on the electrode plate group.
2. Description of the Related Art
As shown in FIG. 14, an electrode plate assembly 1 of a lead accumulator comprises an electrode plate group 10 which is constituted by alternately stacking a plurality of positive and negative electrode plates 3 with interposition of separators 5. Electrode plate leads 6 are formed in projecting manner on each row of the electrode plates 3. The electrode plate assembly 1 is manufactured by effecting connection between respective positive and negative electrode plates 3 by forming respective straps 2 on the positive electrode plate side and negative electrode side on the electrode plate leads 6 and welding the straps 2 and the electrode plate leads 6. Also, pillar electrodes 4 are joined to respective straps 2.
Hereinbelow, for definiteness of the description, the condition in which a plurality of electrode plates 3 are stacked will be referred to as electrode plate group 10, and the condition in which straps 2 and pillar electrodes 4 are formed on this electrode plate group 10 will be referred to as electrode plate assembly 1.
As shown in FIGS. 15A-15D, a conventional method for manufacturing an electrode plate assembly 1 by forming straps 2 and pillar electrodes 4 on electrode plate group 10 is implemented by a manual or automatic welding operation using a welding jig 12 comprising a mating element 7 and a comb element 8. As shown in FIG. 15A, screening between the plate faces of electrode plates 3 and the electrode plate leads 6 is effected by mating the mating element 7 and the comb element 8 with respect to electrode plate leads 6 by inserting the comb teeth of comb element 8 between the row arrangement of electrode plate leads 6, and a pillar electrode 4 is mounted as shown in FIG. 15B in a prescribed position of a recess formed in the external shape of strap 2 on the upper surface of mating element 7 and comb element 8. Next, as shown in FIG. 15C, electrode plate leads 6 projecting into welding jig 12 are heated and melted by burner 9 and a solid lead stock 11 is simultaneously melted by burner 9, causing the lead to flow onto the electrode plate leads 6, thereby filling the recess of the welding jig 12 with melted lead. The shape of straps 2 is thereby formed, and the base of pillar electrode 4 is melted, joining it to strap 2. After the straps 2 have been formed, the welding jig 12 is removed as shown in FIG. 15D. By performing this operation for electrode plate leads 6 of the positive and negative electrodes, an electrode plate assembly 1 as shown in FIG. 14 is formed.
When this welding process is carried out by a manual operation, the worker performs the above operation by holding burner 9 and lead stock 11, and placing welding jig 12 on the electrode plate lead 6 section of electrode plate group 10 and arranging pillar electrode 4 in the prescribed position on welding jig 12.
In contrast, in the case of automatic welding, welding jig 12 and pillar electrode 4 are set in position on electrode plate group 10 fed to the prescribed processing position, and strap 2, joining electrode plate leads 6 and pillar electrode 4, is formed by melting electrode plate leads 6 and a prescribed quantity of lead stock 11 supplied to the recess of welding jig 12.
When the above method of manufacturing an electrode plate group is carried out by a manual operation, differences in the finish are produced by the degree of skill of the worker and a good finished condition has to depend on the "feeling" or "knack" of the worker, so that constant quality is difficult to achieve. Further problems are a working environment in which gas or vapour is generated and poor operating efficiency. In the case where automatic welding is employed, "melting off" (contraction of the lead width) may occur due to local heating of the electrode plate leads 6 caused by misalignment of the feed position of the lead stock 11, and different amounts of lead stock 11 must be prepared for each type of product. Also, although in the manual operation an oxide coating on the surface of the lead can be removed by playing on it the reductive flame produced by burner 9, in the case of automatic welding, the location where the flame plays is automatically controlled, so the range where the oxide coating can be removed is restricted. This leads to the problem of production of bad welds due to unremoved oxide coating.
Accordingly, a method is being developed whereby formation of straps 2 is performed using pre-melted lead rather than solid lead stock 11. When supplying the molten lead, with electrode plate leads 6 of electrode plate group 10 on top, as in the method of manufacture described above, the molten lead penetrates to the electrode plates 3 through gaps between the comb tooth portion of welding jig 12 and electrode plate leads 6. A method has therefore been disclosed in Early Japanese Patent Publication No. 53-36645 in which straps 2 are formed by pouring in molten lead into the mould in which an electrode plate group 10 is set at the location of the electrode plate leads 6, with the electrode plate leads 6 directed laterally in a laterally tipped-over condition.
FIGS. 16A and 16B illustrate this method of manufacture. As shown in FIG. 16A, a strap metal mould 33 is attached to electrode plate leads 6 of an electrode plate group 10 which is tipped over sideways and fixed within a feed box 32, and molten lead 34 is poured into strap metal mould 33. As shown in FIG. 16B, after the lead has been poured in and solidified, the contacts with the solidified lead and the electrode plate leads 6 are re-melted using a plasma welding torch 35, thereby welding these two together.
However, with the method of manufacture using molten lead described above, electrode plate group 10 has to be in a condition tipped over on its side, so it is necessary to change the direction of this sideways tipping over of electrode plate group 10 when strap 2 is formed on the positive electrode side and when strap 2 is formed on the negative electrode side. Thus, in each of the steps of manufacturing a lead accumulator, a step is also required of tipping over and erecting electrode plate group 10. This lowers working efficiency and gives rise to a risk of producing changes in the stacked condition of electrode plates 3. As the size of the lead accumulator increases, the weight of electrode plate group 10 increases and the operation of tipping over and erecting this electrode plate group 10 is not easy. A further problem is that, when the molten lead is poured in, lead oxides and/or scum produced at the surface of the molten lead also get poured in with it, so that straps 2 are formed containing lead oxide and/or scum.